The advantages of vertical pumps are well known in the art. By way of example, because a predominant portion of the vertical pump is commonly installed below ground level, vertical pumps with capacities between one hundred and fifty thousand gallons per minute, may be conveniently employed between horizontal inlet and outlet pipes spaced only a few feet apart. In addition, if pumping head is to be increased, this may be readily accomplished by simply adding stages to the existing pump without altering the pipe assembly leading to and from the pump. In addition, the driver for a vertical pump, which may be an electric motor, a steam turbine, or gas turbine, is readily accessible for easy maintenance and repair. One possible disadvantge of vertical pumps results from the vertical shaft which does not have vertical thrust bearing capacity. Accordingly, a rigid coupling must be utilized to connect the pump shaft to the driver shaft for both radial and axial thrust load bearing.
Rigid coupling assemblies which are designed to transmit the thrust forces of the pump driver to the pump shaft for rotation thereof, while fully bearing the axial thrust loads of the driver that cannot be borne by the pump, are well known in the art. For example, connection of vertical industrial pumps to appropriate drivers, is normally made by using spacer-type adjustable couplings. This is true for all types of vertical pumps, be they turbine type or volute type; be they single or multi-stage units; and whether they use open or closed impellers. A spacer-type coupling is normally required to facilitate the removal of the pump stuffing box components comprising primarily mechanical seals. Adjustment of the coupling is often necessary to locate the pump shaft in its proper vertical position for high speed rotation during pump operation. Furthermore, as previously indicated, the coupling has to be designed to carry axial thrusts.
Successful long term and low cost operation of a vertical pump depends to a great extent on very accurate coupling machining as well as good dynamic balance and extreme care in assembly. Typically, inaccurate machining, or dynamic imbalance, or improper assembly, leads to serious wobble or vibration in the rotating pump system. Such wobble and vibration greatly accelerates the wear and tear of the pump and motor and lead to breakdowns that require extremely difficult, costly, and time consuming repair.
Because of the inherently disadvantageous design of prior art coupling assemblies, dynamic unbalance due to shaft runout remains a problem despite the pump industry's attempts to machine prior art couplings with great accuracy and at commensurately high cost. For example, it is generally accepted in the industry that an acceptable level of shaft runout (in total indicator runout, T.I.R) at the stuffing box face is 0.002 inches. However, in order to maintain such a low runout, the accuracy of all machining of assembly fits, bores, faces, and drilling must be held within plus or minus 0.001 inches. Unfortunately in standard commercial machining shops, it is almost impossible to achieve such accuracies with large diameter registration fits and it is generally impossible to maintain 0.002 inches T.I.R. during operation. The best stuffing box face shaft runout currently available is about 0.007 inches. Even such relatively inaccurate machining is still extremely costly to attain because of the inherent design problems associated with prior art coupling assemblies; and, a shaft runout of 0.007 inches is too high to prevent frequent and costly breakdown and maintenance problems in the field.
The present invention overcomes the aforementioned disadvantages of prior art coupling assemblies by providing a unique coupling configuration that, compared to prior art coupling assemblies, is relatively easy to accurately machine, and thus provide extremely low shaft runout. The present invention, like prior art coupling assemblies, provides means for imparting rotational thrust to the pump shaft, affords a rigid coupling device which bears pump axial thrusts while providing for vertical adjustment of the pump shaft, and still facilitates easy removal of the pump stuffing box components. However, the present invention facilitates highly accurate machining at relatively low cost. Thus, the present invention substantially decreases the liklihood of dynamic unbalance induced by prior art couplings and substantially avoids frequent and costly down-time maintenance problems, as well as pump and driver wear.
The applicant has solved the problems of the prior art coupling assemblies by means of a self-aligning rigid coupling assembly which, unlike the prior art coupling assemblies, does not require accurate registration fits, and does not depend on threading of the shaft. The invention employs small diameter sections that may be accurately machined so that the dynamic unbalance of the prior art is extremely unlikely.
The present invention does away with the multi-flange, large diameter coupling, and large diameter registration fits that are difficult to accurately machine. The present invention employs a comparatively small, constant diameter coupling which includes a pair of rigid hubs separated by adjustment shims and an optional split spacer. Each such component of the novel coupling of the present invention has a diameter which is equal to or less than the maximum diameter of coupling hubs of the prior art.
It is therefore a primary object of the present invention to provide a rigid coupling assembly to couple the shaft of a vertical pump to the co-linearly spaced shaft of the pump driver, but to do so in a manner which overcomes or substantially reduces the disadvantageous high costs and frequent maintenance problems caused by prior art coupling assemblies.
It is a further object of the present invention to provide a spacer-type, adjustable, rigid-split coupling for vertical pumps, the design of which renders it relatively simple to maintain a maximum, total indicator runout of the rotating pump shaft of 0.002 inches at the stuffing box face.
It is still a further object of the present invention to provide a rigid-split coupling for vertical pumps that eliminates all large diameter fits and shaft threading that is typical in prior art couplings.
It is still a further object of the present invention to provide a new coupling assembly of which all parts can be machined from the same diameter forging or tubing and wherein such diameter is sufficiently small to substantially eliminate the liklihood of dynamic unbalance in the rotating shaft-coupling-shaft combination.